[metal bonding method for semiconductor circuit components employing prescribed feeds of metal balls]

ABSTRACT

A method for fabricating metal bonding for a semiconductor circuit component employing prescribed feed of metal ball is disclosed. The method comprises the steps of, first, placing a metal ball at the metallization site on the surface of the circuit die of the component; then, melting the metal ball on the site; and subsequently solidifying the molten metal and forming a metal bump at the site. A circuit die having formed with one or more metal bumps can then be made into a circuit component featuring stable and reliable electrical leads and suitable to be utilized as large power rating yet with reduced component size in electronic equipment.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of a prior application Ser. No.10/249,572, filed Apr. 21, 2003, which claims the priority benefit ofTaiwan application Ser. No. 92106255, filed Mar. 21, 2003.

BACKGROUND OF INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates in general to semiconductor circuitcomponents and a method of fabrication. In particular, the presentinvention relates to the fabrication of metal bonding for device dice ofsemiconductor circuit components utilizing prescribed feeds of metalballs.

[0004] 2. Technical Background

[0005] Core circuit devices of semiconductor circuit components, eitherintegrated or discrete, are fabricated on silicon wafers in batches ofmultiple dice. After the wafer fabrication stage, each circuit componentdie needs to be secured to and hermetically sealed in an enclosure,frequently plastic or ceramic, and becomes a useful circuit componentfor assembly onto the printed circuit board of an electronic equipment.An important step in this packaging process is bonding, the electricalconnection of contact pads on the component die to their correspondingpins of the package.

[0006] Various types of electrical connection are used for differentcircuit components. For example, joining is a scheme connecting the diecircuitry to the package relying on pure mechanically pressed contact.Joining is found primarily in discrete circuit components such as diodesthat mechanically press the electrical contact of a circuit die onto itscorresponding package lead. Joining is susceptible to fluctuations ofenvironmental factors and is generally unreliable.

[0007] Another method of electrical connection between circuit dice andtheir package pins or leads popularly used in integrated circuits andsome discrete components involves the bonding of both the device die andthe die contact pads. The device die is fixedly secured to a substratein the die-bonding process, while wire-bonding connects a length of wireof selected metal or alloy between the contact pads on the circuit dieand their corresponding pins of the package. In the case of ICs, thiswire-bonding facilitates the wired connection between contact padsdistributed around the periphery of the IC die and their correspondingconnection points on the lead-frame of the chip carrier (package).Although straightforward, however, die- and wire-bonding is relativelytedious, time-consuming and costly as mechanical maneuvering isnecessary for each bonding.

[0008] Note that bonding provided by hardened metal grain-containingbonding pastes can not be considered metal bond. The resin-basedmaterial embedding the metal grains is susceptible to changes inenvironmental factors, temperature and humidity in particular. More,these conventional methods, die-/wire-bonding and similar inclusive, arenot suitable for large-power applications such as power diodes.

[0009] Some prior-art components, power transistor and diodes inparticular, require the stability and strong bond provided by metalbonding due to thermal stresses arising from their operation. However,conventional metal bonding has been relying on rare and expensive metalssuch as rhodium, molybdenum and platinum so that manufacturing costs arehigh.

SUMMARY OF INVENTION

[0010] It is therefore an object of the present invention to provide amethod of fabricating metal bonding for semiconductor circuit componentsbetween die electrical contacts and package electrical leads that isreliable within the temperature ranges during both fabrication andoperation of circuit components.

[0011] It is another object of the present invention to provide a methodof fabricating reliable metal bonding for semiconductor circuitcomponents at low costs.

[0012] In order to achieve the above and other objects, the presentinvention provides a method for the fabrication of metal bonding for asemiconductor circuit component employing prescribed feed of metal ball.The metal bonding frabrication method comprises the steps of, first,placing a metal ball at the metallization site on the surface of thecircuit die of the component; then, melting the metal ball on the site;and subsequently solidifying the molten metal and forming a metal bumpat the site.

BRIEF DESCRIPTION OF DRAWINGS

[0013] The above and other objects, features, and advantages of thisinvention will become apparent by way of the following detaileddescription of the preferred but non-limiting embodiments. Thedescription is made with reference to the accompanying drawings inwhich.

[0014]FIG. 1 is a cross-sectional view showing a semiconductor wafer forthe manufacture of circuit components featuring metal bonding inaccordance with a preferred embodiment of the present invention.

[0015]FIG. 2 is a cross-sectional view showing the placement of one feedof bonding metal on the surface of each unit of circuit die of thewafer.

[0016]FIG. 3 is a cross-sectional view showing the melt-bonding of eachmetal ball feed of FIG. 2 onto the surface of the corresponding unit ofcircuit die of the wafer.

[0017]FIG. 4 is a cross-sectional view illustrating the separation ofthe circuit dice from the gross wafer of FIG. 3.

[0018]FIG. 5 is a cross-sectional view illustrating the individualcircuit dice formed as a result of the separation implemented in FIG. 4.

[0019]FIG. 6 is a cross-sectional view illustrating the placement of onecircuit die with a metal bump formed to one surface thereof into onecorresponding recessed space formed over the surface of a fixture.

[0020]FIG. 7 is a top view illustrating the placement of one feed ofbonding metal on the surface of each unit of circuit die as settled inthe corresponding recessed space thereof.

[0021]FIG. 8 is a cross-sectional view illustrating the orderlyplacement of one feed of bonding metal ball onto the surface of onecircuit die placed in the recessed space of the fixture.

[0022]FIG. 9 is a cross-sectional view illustrating the melt-bonding ofeach metal ball feed of FIG. 8 onto the surface of the correspondingunit circuit die placed in the corresponding recessed space of thefixture.

[0023]FIG. 10 is a cross-sectional view illustrating the formation ofone metal bump on each of the two opposite surfaces of a diode with aplanar P/N junction after physically separated into one individual die.

[0024]FIG. 11 is a cross-sectional view illustrating the formation ofone metal bump on each of the two opposite surfaces of a diode with aplanar P/N junction after physically separated into one individual die.

[0025]FIG. 12 is a cross-sectional view illustrating the formation ofone metal bump on each of the two opposite surfaces of a diode with amesa P/N junction after physically separated into one individual die.

DETAILED DESCRIPTION

[0026] The present invention discloses a method for fabricating metalbonding for semiconductor circuit components that employs prescribedfeeds of metal balls, which allow for the manufacture of componentshaving strong and stable metal bonds. Although discrete circuitcomponents are used in the following descriptive paragraphs for thedescription of the present invention, the method of the presentinvention, however, is equally suitable for application to integratedcircuits.

[0027] Also, the method of the present invention can be tightly combinedwith the semiconductor wafer fabrication stage of the manufacture of acircuit component. In other words, method procedural steps of thepresent invention can be adequately intermixed and integrated with thewafer fabrication of the target circuit dice. On the other hand, themethod of the present invention can also be initiated after thefabrication of a wafer of the target circuit dice has generally beenconcluded. The method of the present invention then takes such a waferas input for processing. Thus, the method of the present inventionessentially does not interfere with the semiconductor fabricationprocessing. Rather, it can be considered as a succeeding processing thatadd to the target circuit component the valuable characteristics ofmetal bonding.

[0028] More, the metal described in the following embodiments of thepresent invention can be any metal or alloy suitable for the purpose ofproviding electrically conductive bonding between the circuit die andthe electrical leads of its protective packaging. Preferred metals arethose having a melting temperature sufficiently above the designedoperating temperature and below the semiconductor fabrication processingtemperature range of the target component.

[0029] As indicated, discrete circuit components are used as examplesfor the description of the present invention. FIG. 1 illustrates across-sectional view showing a semiconductor wafer for the manufactureof circuit components featuring metal bonding in accordance with apreferred embodiment of the present invention. A section of a wafer 100including a number of units of circuit dies 110 not yet physicallyseparated is shown in the cross-sectional view. Note that details of thesemiconductor structural configuration of each die 110 (which may, forexample, be a diode) are not elaborated in the drawing as they are notthe subject matter of the present invention.

[0030] Top surface of each die 110 in FIG. 1 has a metallization surfacearea ready to accept the placement of one feed of metal ball 120 as isshown in FIG. 2. Before the placement of the feeds 120, the location ofball placement for each unit die 110 can be prepared with a coating ofbonding flux via, for example, a screen-printing process. This assistsin the temporary secured attachment of each of the placed feeds of metalballs 120 before melted to inflict a true metal bonding between the feedof metal 120 and the metallization surface of the die 110. The coatedflux itself can also assists in the metal bonding.

[0031] It should also be mentioned that the gross placement of an entirematrix of feed balls over the surface of a wafer such as illustrated inFIG. 2 is achievable via mechanical manipulations involving, forexample, the shaking of the balls after they are poured thereon.Although not detailed in FIGS. 1 and 2, the top surface of each of thedice where a metal feed ball is to be placed, selective surfacecharacteristics of the wafer assists in achieving the placement of oneand only one ball for each die.

[0032] Then, the wafer 100 of FIG. 2, together with its placement ofmatrix of metal feed balls 120, can be subject to a thermal processingscheme that melts all the balls on-site their respective placementlocation, as is illustrated in FIG. 3. The thermal processing to meltthe feed balls may, for example, be a thermal reflow. In the drawing,the cross-sectional view shows the melt-bonding of each metal ball feedof FIG. 2 results into a metal bump 122 on top the surface of thecorresponding unit of circuit die 110 of the wafer 100. Note that thesize of the bump 122 can be easily controllable by selecting the size ofthe balls 120. Also, shapes of all the bumps 122 for the entire matrixcan be within a high degree of uniformity.

[0033] As mentioned, the metal or alloy selected for the balls 120 has amelting temperature sufficiently above the designed operatingtemperature range and below the semiconductor fabrication processingtemperature range of the target component.

[0034] After the formation of the metal bumps 122 in FIG. 3, the wafer100 of FIG. 3 can then be submitted for a cutting procedure thatphysically separates all individual dice from the gross wafer, as isillustrated in FIG. 4. FIG. 4 is a cross-sectional view illustrating thelocations of separation of the circuit dice from the gross wafer of FIG.3. The result of this separation is illustrated in FIG. 5 as individualsingle-bump dice 112.

[0035] If the design of a circuit component requires that the die hasone single metal bump, the individual dice as cut from the wafer andshown in FIG. 5 can then be sent for the packaging procedural steps, andthe metal-bonding processing of the present invention concludes. Thepost processing of the circuit dices eventually results into completecircuit components equipped with stable and reliable metal bonding.

[0036] If, however, each of the target circuit dice needs two or moremetal bumps, the processing of the present invention continues from FIG.3 as illustrated in FIG. 6. FIG. 6 is a cross-sectional viewillustrating the placement of one circuit die with a metal bump formedto one surface thereof into one corresponding recessed space formed overthe surface of a fixture. As is illustrated in the cross-sectional view,the fixture 140 provides an entire array of spaces 144, each of whichcan be used to accommodate one circuit die 112. A plain view of thefixture can be seen in FIG. 7 to be described below.

[0037] As is illustrated, each of the circuit die 112 falling into itscorresponding space 144 in the fixture 140 has its metal bump 122 facingdownward.

[0038] The second metal bump can then be formed for each of the circuitdie already placed in its corresponding space within the fixture, as isillustrated in FIG. 7. FIG. 7 is a top view illustrating the placementof one feed of bonding metal on the surface of each unit of circuit diesettled in the corresponding space thereof. One and only one metal feedball 160 is placed on the designated site over the surface of a circuitdie 112. As is shown, each of the dice 112 is in turn placed within itsspace 144 of the fixture 140.

[0039]FIG. 8 is a cross-sectional view illustrating the orderlyplacement of one feed of bonding metal ball onto the surface of onecircuit die placed in the corresponding space of the fixture. Topsurface of the die 112, similar to that described above for theformation of the first metal bump, can also assist in the alignedplacement of the feed ball onto the die.

[0040] A thermal processing scheme, a thermal reflow for example, thenfollows to melt each of the placed metal feed balls. FIG. 9 is across-sectional view illustrating the melt-bonding of each metal ballfeed of FIG. 8 onto the surface of the corresponding unit circuit die.Result of the thermal processing is a second metal bump 162 for each ofthe processed dice 112.

[0041] Note that the size and shape of this second metal bump 162 foreach die 112 can be different from its first bump 122, as is illustratedin FIG. 9. Again, the size of this second bump 162 is also controllablevia adjustment of the second metal feed balls 160, it is also equallyapplicable that if the second bump is required to be of the same size asthat of the first. Shape of the bumps among all dice would also beuniform.

[0042] Shape and size of the metal bumps are controllable via selectionof the size, weight and/or material of the metal ball feeds. Suchcontrol can be advantageous in the fabrication of certain discretecomponents such as, for example, diodes and transistors. For example,P/N polarities of a batch of diodes fabricated can be easily aligned inuniformity by arranging different size and or weight of the respectivemetal bumps formed on the opposite surfaces of each of the device die.

[0043]FIGS. 10, 11 and 12 respectively depicts the cross-section view ofdice of three types of diode made with metal bumps in accordance withthe present invention that can be used to form metal bonding in theirrespective packaging. FIG. 10 is a cross-sectional view illustrating theformation of one metal bump, 1022 and 1062 respectively, on each of thetwo opposite surfaces of a diode 1012 with a planar P/N junction afterphysically separated into one individual die. FIG. 11 is across-sectional view illustrating the formation of one metal bump, 1122and 1162 respectively, on each of the two opposite surfaces of a diode1112 with a planar P/N junction after physically separated into oneindividual die. And, FIG. 12 is a cross-sectional view illustrating theformation of one metal bump, 1222 and 1262 respectively, on each of thetwo opposite surfaces of a diode 1212 with a mesa P/N junction afterphysically separated into one individual die.

[0044] The above descriptive paragraphs, together with the accompanyingdrawings, describe a general method for the fabrication of metal bondingof a semiconductor circuit component employing prescribed feed of metalball. An inventive method in accordance with the teaching of the presentinvention thus comprises the steps of, first, placing a metal ball atthe metallization site on the surface of the circuit die of thecomponent; then, melting the metal ball on the site; and subsequentlysolidifying the molten metal and forming a metal bump at the site.

[0045] As is comprehensible, different metallic material such as,copper, aluminum, tin and lead and the their alloy are applicable foruse in a process of the present invention for forming metallic bumps.

[0046] Metal bonding is a more reliable method of die-package electricalconnection than others. Metal bonds are stable and therefore securewithin the typical operating temperature range (about 200 to 700 degreeCelsius) of semiconductor components. On the other hand, the temperaturerange for the formation of metal bonds is normally well below thetemperatures for typical semiconductor fabrication processing. Thus,metal bonding processing steps implemented after the fabrication ofcircuit die is concluded in a semiconductor facility is advantageous.This is because the metal-bonding processing does not damage the die dueto the fact that the thermal-based processing temperature range formetal bonding is typically well below that for the die fabrication.Further, since only thermal processing is required without theinvolvement of any acid and/or base treatments, the metal bonding inaccordance with the teaching of the present invention has little, if anyat all, effect on the quality of the circuit die obviously moreenvironmental-friendly.

[0047] While the above is a full description of the specific embodimentsof the present invention, various modifications, alternativeconstructions and equivalents may be used. Therefore, the abovedescription and illustrations should not be taken as limiting the scopeof the present invention which is defined by the appended claims.

11. A semiconductor circuit component comprising a circuit die, saidcircuit die having at least one electrical contact area for connectionto the packaging of said semiconductor circuit component, said at leastone electrical contact area being bond to the corresponding lead of saidpackaging by metallic material formed by a metal ball of prescribed feedmelted during the fabrication of said component.
 12. The semiconductorcircuit component of claim 11, wherein said metal ball contains copper.13. The semiconductor circuit component of claim 11 wherein said metalball contains aluminum.
 14. The semiconductor circuit component of claim11, wherein said metal ball contains tin.
 15. The semiconductor circuitcomponent of claim 11, wherein said metal ball contains lead.
 16. Thesemiconductor circuit component of claim 11, further comprising a secondmetal bump.
 17. The semiconductor circuit component of claim 16, whereinsaid two metal bumps being of different sizes.
 18. The semiconductorcircuit component of claim 16, wherein said two metal bumps being ofdifferent shapes.
 19. The semiconductor circuit component of claim 16,wherein said two metal bumps being made of different materials.
 20. Thesemiconductor circuit component of claim 11, further comprising at leastone more metal bump.